Background: A late-relapse germ cell tumor (GCT) might contain malignant non-germ cell tumor cells, known as „somatic-type malignancy” (SM). Development of secondary SM is extremely rare and occurs in only 1% of patients with GCT.
Case study: We present the case of a 42-year-old patient who developed retroperitoneal tumor with duodenal and right colon involvement 6 years after he underwent left orchidectomy for stage IIC mixed GCT (95% seminoma, 5% teratoma). Since the tumor markers for germline tumor were normal, another type of tumor was highly suspected, most likely a malignant alteration of the residual teratoma. Tumor was completely removed and pathological report suggested undifferentiated sarcoma.
Conclusion: R0 resection and postoperative patient follow-up by the protocol for at least 6 years after orhidectomy is the key to successful treatment of GCT. Malignant tumor transformations are rare, but still possible so clinicians should be aware of the importance of frequent and adequate patient monitoring
